1. Field of the Invention
The invention relates to optical networking components. In particular, the invention relates to optical filters.
2. Background of the Invention
Optical networks often include optical fibers for carrying light signals having a plurality of channels. Each of the channels is generally associated with a particular wavelength or a particular range of wavelengths. These networks typically employ optical filters for filtering light signals having particular wavelengths from a multichannel light signals. The range of wavelengths that is filtered by a particular optical filter is called the bandwidth of the optical filter.
A tunable filter is a variety of optical filter that allows the band of wavelengths that is filtered to be tuned. The turning range of most tunable filter is not wide enough to cover C or L band, and the bandwidth of many tunable filters changes as the filter is tuned. As a result, the performance of the optical filter is inconsistent across the tuning range of the optical filter. Further, many optical filters have undesirably large power requirements.
For the above reasons, there is a need for a tunable optical filter having a wide turning range. There is also a need for a tunable optical filter having a bandwidth that is substantially stable through the tuning range of the filter and/or that has reduced power requirements.
The invention relates to an optical filter system. The optical filter system includes a first filter configured to output light signals having wavelengths falling within a plurality of periodically spaced wavelength bands. A second filter is in optical communication with the first filter and is configured to output light signals having wavelengths falling within a plurality of periodically spaced bands. The period of the bands associated with the first filter is different than the period of the bands associated with the second filter.
In some instances, the selection of wavelengths that fall within the wavelength bands of the first filter is tunable while the selection of wavelengths that fall within the wavelength bands of the second filter is not tunable. In yet another embodiment, the selection of wavelengths that fall within the wavelength bands of the first filter is tunable and the selection of wavelengths that fall within the wavelength bands of the second filter is tunable.
In another embodiment of the system, the first filter is configured to output light signals having wavelengths falling within one or more wavelength bands. The wavelengths that fall within the one or more bands is tunable. A second filter in optical communication with the first filter and is configured to output light signals having wavelengths falling within a plurality of periodically spaced wavelength bands.
The system can be configured such that the first filter receives the light signals output by the second filter or such that the second filter receives the light signals output by the first filter.
In some instances, the width of the bands of the first filter is different from the width of the bands of the second filter.
In one embodiment of the invention, an optical fiber connects an optical component having the first filter to an optical component having the second filter. The optical fiber providing optical communication between the first filter and the second filter. Alternatively, the first filter and the second filter are positioned on the same optical component.
In another embodiment of the invention, the first filter includes a first array waveguide grating having a plurality of first array waveguides. At least a portion of the first array waveguides can include an effective length tuner for changing the effective length of an array waveguide. In some instances, an end of each first array waveguide includes a reflector for reflecting a light signal traveling toward the reflector along the first array waveguide back into the first array waveguide. Additionally or alternatively, the second filter can include a second array waveguide grating having a plurality of second array waveguides. At least a portion of the second array waveguides can include an effective length tuner for changing the effective length of an array waveguide. In some instances, an end of each second array waveguide includes a reflector for reflecting a light signal traveling toward the reflector along the second array waveguide back into the second array waveguide.
In one embodiment, the first filter includes a first array waveguide grating connected to a light distribution component and the second filter includes a second array waveguide grating connected to the light distribution component. In some instances, a transition waveguide connects one region of the light distribution component to another region of the light distribution component.
The invention also relates to a method of operating an optical filter system. The method includes selecting a target wavelength to be produced by an optical filter system. The optical filter system has a first filter in optical communication with a second filter. The first filter is configured to output light signals having wavelengths falling within one or more wavelength bands. The second filter is configured to output light signals having wavelengths that overlap with the target wavelength. The method also includes tuning the first filter such that a band of the first filter overlaps with the target wavelength.
Another embodiment of the method includes selecting a target wavelength to be produced by the optical filter system. The system having a first filter in optical communication with a second filter. The first filter is configured to output light signals having wavelengths falling within one or more bands. The second filter is configured to output light signals having wavelengths that fall within one or more bands. The method also includes tuning the first filter such that a band of the first filter overlaps with the target wavelength. The method further includes tuning the second filter such that a band of the second filter overlaps with the target wavelength.
The system can be configured such that the first filter can be configured to receive the light signals output by the second filter or the second filter can be configured to receive the light signals output by the first filter.